The power semiconductor switching devices with which we are particularly concerned typically have a current carrying capability of greater than 1 amp and are operable with a voltage of greater than 100 volts. Embodiments of the devices with which we are concerned are able to carry currents of greater than 10 amps, 50 amps or 100 amps and/or are able to sustain a voltage difference across the device of greater than 500 volts or 1 KV.
Examples of such devices include insulated gate bipolar transistors (IGBTs), as well as FETs such as MOSFETS (vertical or lateral) and JFETs, and potentially devices such as LILETs (lateral inversion layer emitter transistors), GTOs (Gate Turn-Off thyristors). IGCTs (Integrated Gate Commutated Thyristors) and the like. The techniques we will describe are not limited to any particular type of device architecture and thus the power switching devices may be, for example, either vertical or lateral devices; they may be fabricated in a range of technologies including, but not limited to, silicon, and silicon carbide.
Switching devices of this type have applications which include switching in high voltage transmission lines, in particular dc transmission lines of the type which may, for example, carry power from an offshore wind installation, and medium voltage (for example greater than 1 KV) switching for motors and the like, for example locomotive motors.
There are particular problems in controlling such devices, in part because the high currents/voltages involved mean that an error, for example, an error in the control system or excessive power dissipation or over voltage of a power switching device, can have potentially serious consequences. In addition these devices often operate in electrically noisy environments and, further, 10s or 100s of devices may be connected in series and/or parallel to achieve the desired ratings. In such an arrangement switching of the devices needs to be carefully synchronised. It is also preferable that the control techniques can address a situation where one of many connected devices fails.